1. Field of the Invention
The present invention relates to a visible laser-curable composition. More particularly, the present invention relates to a visible laser-curable composition having very high sensitivity to a laser beam having a wavelength of 488 nm.
2. Description of the Prior Art
In recent years, visible laser-curable compositions have come to be used as image-forming photosensitive materials such as photoresist, plate material and the like. A method for image formation by direct writing using a light source of high energy density, for example, a laser, has merits in that not only the energy conversion efficiency is high but also the image-forming step is significantly simplified.
Hence, it is desired to develop a visible laser-curable composition which has high sensitivity to and can be subjected to scanning exposure with a visible laser giving an oscillation line stable in durability and intensity, particularly an Ar laser having a stable oscillation line in a visible wavelength region of 488 nm or 514.5 nm.
Various proposals were made to respond to the above demand. For example, compositions using a photopolymerization inititor system consisting of a particular ketocoumarin type sensitizer and a polymerization initiator are disclosed in Japanese Patent Application Laid-Open No. 223759/1991 (corresponding to U.S. Pat. No. 5,045,434), Japanese Patent Application Laid-Open No. 301208/1994, Japanese Patent Publication No. 9644/1996, etc.
The above compositions using a photopolymerization initiator system have polymerization initiatability to a light of visible region; however, their sensitivity is not sufficient and need to be improved for laser curing which is complete in a very short period of time. Therefore, it is desired in the art to develop a more practical photopolymerization initiator system having higher sensitivity.